Technical Abstract:
A biological filter is an essential component of recirculating aquaculture systems because it facilitates the oxidation of ammonia (NH3-N) to nitrite (NO2-N) and then to nitrate (NO3-N) by autotrophic bacteria (Nitrosomonas and Nitrobacter). Ammonia and nitrite are toxic compounds and the health of the fish in the culture system depends on the ability of a biological filter to convert ammonia rapidly to nitrate which is relatively non-toxic. The main sources of ammonia in a system are decaying organic matter and the metabolic by-products of the species in the culture system. Nitrifying bacteria have slow growth rates, thus the time it takes for a new biological filter to reach full nitrifying capacity is lengthy. Experimenters have found that this two-step oxidation of ammonia to nitrite and then nitrate in a biological filter usually takes from 30 to 60 days, with startup taking longer at lower temperatures. Generally a 'seed' of bacteria for a new filter is obtained by transferring medium from an existing filter. Although this method seems obvious that it will activate the medium of a new filter faster, there is little evidence that such a procedure is effective. There is a lack of literature providing tested
methods for decreasing the time to complete the nitrification establishment in a new biological filter, especially with the use of chemical additives. This study examines the acclimation response for experimental submerged biofilters to commercial additives containing nitrifying bacteria that are used to accelerate filter startup in a commercial setting. Three commercial additives, and seeded media were evaluated for accelerated nitrification establishment of experimental submerged biofilters (11 L) set up in a 100 liter aquaria with a system turnover rate of once per hour. Unseeded new media was set up as the control and each treatment was evaluated in triplicate. Ammonia chloride (NH4CL) was used to inoculate the system and provide a total ammonia nitrogen concentration
of approximately 3 mg/L. Systems were reinoculated to 2.0 mg/L TAN after TAN concentrations dropped below 1.0 mg/L. After 45 days the experiment was concluded and results evaluated. The introduction of chemical additives or seeded media did not accelerate the nitrification process in the new submerged biological filters.